1. Field of the Invention
The present invention relates generally to systems and methods for use in the precision cleaning of substrate surfaces, such as delicate surfaces and precision parts. More particularly, the present invention relates to an improved system for removing trace contaminants from the surface of a substrate, such as delicate surfaces or precision hardware, for example, those found in high sensitivity optical, electronic and precision mechanical equipment.
2. Description of Related Art
It is essential that the delicate and precision surfaces of optical-mechanical-electronic equipment be contaminant-free. For example, infrared optical sensor systems use thin film optical coatings to enhance in-band transmittance and reject out-of-band radiation. Even trace amounts of contamination degrade spectral performance by scattering, absorbing, or reflecting incident radiation.
The particulate and molecular contaminants present on optical surfaces can cause problems by changing emittance characteristics thereby increasing thermal noise in optical devices. Dust and debris contamination present on a detector surface may also generate clutter and the appearance of false targets. Further, the presence of molecular contaminants on precision optical equipment surfaces, such as lenses, windows and optical filters, results in the absorption and scatter of incident energy with the resultant decrease in system quality. In addition, in precision computer and gyroscope equipment, particle contamination in a moving disk drive or in a spinning gyroscope stator may damage or disable such a system beyond repair.
A wide variety of cleaning solvents and solutions, such as chlorofluorocarbons and ketones, have been utilized to clean delicate surfaces. However, the majority of these cleaning solutions and solvents are environmentally hazardous. In response to these environmental concerns, a number of environmentally safe cleaning materials have been proposed. One particular cleaning material which has been investigated is carbon dioxide. A variety of investigators have reported cleaning various parts utilizing a stream or jet spray of carbon dioxide. The jet stream of carbon dioxide, also known as "dry ice snow", has been used to remove light oils and particulate contaminants from surfaces. Such carbon dioxide jet sprays have been used to clean contaminants from a variety of surfaces including silicon wafers, telescope mirrors and thin film optical coatings.
The use of carbon dioxide snow to clean delicate surfaces has shown promise. However, as with any new cleaning system, there is a continual need to further develop and improve upon existing systems and procedures. For example, many of the contaminants removed from delicate or precision surfaces during carbon dioxide cleaning contain highly toxic or radioactive materials such as selenium, arsenic, cadmium, thorium and beryllium. There are numerous other organic and inorganic materials and dusts which must be removed from delicate and precision surfaces and which are toxic and unsafe. It is important that these types of contaminants be prevented from escaping into the environment during the cleaning process.
Another area which is in need of continual improvement involves increasing the efficiency of the carbon dioxide cleaning process while at the same time preventing or reducing damage to delicate surfaces. There is also a continuing need to provide improved systems and methods which are capable of utilizing carbon dioxide snow and snow produced by other gases in an efficient manner to provide ultra-cleaning of a wide variety of different contaminants from delicate and precision surfaces. Such systems should not only be versatile and efficient, but should also be capable of preventing the escape of toxic contaminants into the environment. Finally, continued improvement of carbon dioxide cleaning processes requires that a means be provided to monitor the effectiveness of the cleaning process to determine when the part has been adequately cleaned so that the cleaning process can be terminated.